Cutting tools

ABSTRACT

A cutting tool comprising a base material and a coating arranged on the base material; wherein: the coating comprises an α-Al2O3 layer composed of a plurality of α-Al2O3 particles; the average particle diameter a of the α-Al2O3 particles in a first region of the α-Al2O3 layer is 0.10 μm or more and 0.30 μm or less; the average particle diameter b of the α-Al2O3 particles in a second region of the α-Al2O3 layer is 0.30 μm or more and 0.50 μm or less; the average particle diameter c of the α-Al2O3 particles in a third region of the α-Al2O3 layer is 0.10 μm or more and 0.30 μm or less; and the ratio b/a is 1.5 or more and 5.0 or less.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on PCT filing PCT/JP2021/011652, filedMar. 22, 2021, the entire contents of which are incorporated herein byreference. This application is also related to U.S. patent applicationSer. No. 17/439,410, entitled Cutting Tools, filed on Sep. 15, 2021, andU.S. patent application Ser. No. 17/439,417, entitled Cutting Tools,filed on Sep. 15, 2021, both of which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure relates to cutting tools.

BACKGROUND ART

Cutting tools having a coating formed on a base material have beenconventionally used. Aluminum oxide having an α-type crystal structure(hereinafter also referred to as “α-Al₂O₃”) has been used as a coatingmaterial, due to its excellent mechanical properties (see JapanesePatent Laying-Open No. 6-316758 (PTL 1) and Japanese Patent Laying-OpenNo. 2013-111720 (PTL 2)).

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laying-Open No. 6-316758

PTL 2: Japanese Patent Laying-Open No. 2013-111720

SUMMARY OF INVENTION

The cutting tool of the present disclosure is a cutting tool comprisinga base material and a coating arranged on the base material; wherein:

the coating comprises an α-Al₂O₃ layer;

the α-Al₂O₃ layer is composed of a plurality of α-Al₂O₃ particles;

the α-Al₂O₃ layer comprises a first region, a second region and a thirdregion;

the first region is a region sandwiched between an interface P1 on thebase material side of the α-Al₂O₃ layer and a virtual surface S1 that islocated at a distance of 0.5 μm from interface P1 toward the surfaceside of the coating;

the second region is a region sandwiched between virtual surface S1 anda virtual surface S2 that is located at a distance of 1.0 μm fromvirtual surface S1 toward the surface side of the coating;

the third region is a region sandwiched between a surface P2 of theα-Al₂O₃ layer or an interface P3 on the surface side of the coating ofthe α-Al₂O₃ layer and a virtual surface S3 that is located at a distanceof 1.0 μm from surface P2 or from interface P3 toward the base materialside;

the average particle diameter a of the α-Al₂O₃ particles in the firstregion is 0.10 μm or more and 0.30 μm or less;

the average particle diameter b of the α-Al₂O₃ particles in the secondregion is 0.30 μm or more and 0.50 μm or less;

the average particle diameter c of the α-Al₂O₃ particles in the thirdregion is 0.10 μm or more and 0.30 μm or less; and

the ratio b/a between the average particle diameter b and the averageparticle diameter a is 1.5 or more and 5.0 or less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an example of a cross section of acutting tool according to Embodiment 1.

FIG. 2 is a schematic diagram showing another example of a cross sectionof a cutting tool according to Embodiment 1.

FIG. 3 is a schematic diagram showing another example of a cross sectionof a cutting tool according to Embodiment 1.

FIG. 4 is a schematic diagram showing another example of a cross sectionof a cutting tool according to Embodiment 1.

FIG. 5 is a diagram schematically showing an example of a backscatteredelectron image of an α-Al₂O₃ layer.

FIG. 6 is a diagram illustrating a method for measuring the averageparticle diameter of an α-Al₂O₃ layer.

FIG. 7 is a diagram illustrating a method for measuring the averageparticle diameter of an α-Al₂O₃ layer.

DESCRIPTION OF EMBODIMENTS Technical Problem

An α-Al₂O₃ layer is excellent in mechanical properties, but requiresfurther improvement in adhesion to the other layers and in fractureresistance. In addition, high-hardness steel also requires furtherimprovement in wear resistance. Therefore, an object of the presentdisclosure is to provide a tool having a long tool life even inhigh-efficiency machining of high-hardness steel.

Advantageous Effects of Invention

The cutting tool of the present disclosure can have a long tool lifeeven in high-efficiency machining of high-hardness steel.

DESCRIPTION OF EMBODIMENTS

First, Embodiments of the present disclosure will be listed andillustrated.

(1) The cutting tool of the present disclosure is a cutting toolcomprising a base material and a coating arranged on the base material;wherein:

the coating comprises an α-Al₂O₃ layer;

the α-Al₂O₃ layer is composed of a plurality of α-Al₂O₃ particles;

the α-Al₂O₃ layer comprises a first region, a second region and a thirdregion;

the first region is a region sandwiched between an interface P1 on thebase material side of the α-Al₂O₃ layer and a virtual surface S1 that islocated at a distance of 0.5 μm from interface P1 toward the surfaceside of the coating;

the second region is a region sandwiched between virtual surface S1 anda virtual surface S2 that is located at a distance of 1.0 μm fromvirtual surface S1 toward the surface side of the coating;

the third region is a region sandwiched between a surface P2 of theα-Al₂O₃ layer or an interface P3 on the surface side of the coating ofthe α-Al₂O₃ layer and a virtual surface S3 that is located at a distanceof 1.0 μm from surface P2 or from interface P3 toward the base materialside;

the average particle diameter a of the α-Al₂O₃ particles in the firstregion is 0.10 μm or more and 0.30 μm or less;

the average particle diameter b of the α-Al₂O₃ particles in the secondregion is 0.30 μm or more and 0.50 μm or less;

the average particle diameter c of the α-Al₂O₃ particles in the thirdregion is 0.10 μm or more and 0.30 μm or less; and

the ratio b/a between the average particle diameter b and the averageparticle diameter a is 1.5 or more and 5.0 or less.

The cutting tool of the present disclosure can have a long tool lifeeven in high-efficiency machining of high-hardness steel.

(2) The average particle diameter c is preferably 0.16 μm or more and0.24 μm or less. This results in improved wear resistance of the cuttingtool.

(3) The ratio b/a is preferably 1.5 or more and 2.5 or less. Thisresults in improved adhesion between the first region and the secondregion and improved fracture resistance.

(4) The average thickness of the α-Al₂O₃ layer is 3 μm or more and 15 μmor less. This can result in both excellent wear resistance and fractureresistance at the same time.

(5) The α-Al₂O₃ layer preferably has a TC (0 0 12) of 3 or more in anorientation index TC (hkl). This results in improved wear resistance ofthe cutting tool.

DETAILS OF EMBODIMENTS

In order to develop a tool capable of having a long tool life even inhigh-efficiency machining of high-hardness steel, the present inventorshave used the conventional cutting tools described in PTL 1 and PTL 2 toperform high-efficiency machining of high-hardness steel and observe thestate of the tools after machining.

The cutting tool in PTL 1 has had a large amount of wear. This has beenpresumed to be because the cutting tool in PTL 1 has a relatively largeparticle diameter of the alumina layer of 0.5 μm to 3 μm.

The cutting tool in PTL 2 has tended to easily fracture. This has beenpresumed to be because the cutting tool in PTL 2 will have a largedifference between the particle diameter on the lower side of an aluminalayer and that on the surface side of the alumina layer and an interfacebetween crystal particles will thereby occur at the boundary between thelower side and the upper side of the alumina layer, resulting in crackextension starting from the interface.

The present inventors have diligent studies based on the above findingsand as a result, have completed a cutting tool of the present disclosurehaving excellent wear resistance and fracture resistance and having along tool life. Specific examples of the cutting tool of the presentdisclosure will be described below with reference to the drawings. Inthe drawings of the present disclosure, the same reference signs referto the same parts or equivalent parts. The dimensional relationshipsamong length, width, thickness, depth and the like are changed asappropriate for the purpose of clarifying and simplifying the drawings,and do not necessarily correspond to the actual dimensionalrelationships.

The expression “A to B” as used herein means the upper and lower limitsof the range (that is, A or more and B or less), wherein when the unitis described only for B but not for A, the unit of A is the same as thatof B.

In the case of representing a compound or the like by a chemical formulain the present specification, when the atomic ratio is not particularlylimited, the formula is intended to include any atomic ratioconventionally known and is not necessarily limited to that in astoichiometric range. For example, when “TiCN” is described, the ratioof the numbers of atoms constituting TiCN includes any atomic ratioconventionally known.

Embodiment 1: Cutting Tool

The cutting tool of one embodiment of the present disclosure(hereinafter also referred to as “present embodiment”) is a cutting toolcomprising a base material and a coating arranged on the base material;wherein:

the coating comprises an α-Al₂O₃ layer;

the α-Al₂O₃ layer is composed of a plurality of α-Al₂O₃ particles;

the α-Al₂O₃ layer comprises a first region, a second region and a thirdregion;

the first region is a region sandwiched between an interface P1 on thebase material side of the α-Al₂O₃ layer and a virtual surface S1 that islocated at a distance of 0.5 μm from interface P1 toward the surfaceside of the coating;

the second region is a region sandwiched between virtual surface S1 anda virtual surface S2 that is located at a distance of 1.0 μm fromvirtual surface S1 toward the surface side of the coating;

the third region is a region sandwiched between a surface P2 of theα-Al₂O₃ layer or an interface P3 on the surface side of the coating ofthe α-Al₂O₃ layer and a virtual surface S3 that is located at a distanceof 1.0 μm from surface P2 or from interface P3 toward the base materialside;

the average particle diameter a of the α-Al₂O₃ particles in the firstregion is 0.10 μm or more and 0.30 μm or less;

the average particle diameter b of the α-Al₂O₃ particles in the secondregion is 0.30 μm or more and 0.50 μm or less;

the average particle diameter c of the α-Al₂O₃ particles in the thirdregion is 0.10 μm or more and 0.30 μm or less; and

the ratio b/a between the average particle diameter b and the averageparticle diameter a is 1.5 or more and 5.0 or less.

The cutting tool of the present embodiment can have a long tool lifeeven in high-efficiency machining of high-hardness steel. The reasonsare not clear but are presumed to be as described below in (i) to (iii).

(i) In the cutting tool of the present embodiment, the average particlediameter a of the α-Al₂O₃ particles in the first region of the α-Al₂O₃layer (hereinafter as referred to as “average particle diameter a of thefirst region” is as small as 0.10 μm or more and 0.30 μm or less. Thisresults in a large adhesion between the α-Al₂O₃ layer and a layer incontact with the base material side of the α-Al₂O₃ layer (hereinafteralso referred to as “underlayer”) or the base material in contact withthe α-Al₂O₃ layer. Therefore, at the time of cutting, the cutting tooldoes not easily cause crack extension starting from the interfacebetween the α-Al₂O₃ layer and the underlayer or the base material andhas thereby excellent fracture resistance. In addition, the averageparticle diameter a of the first region in the above range providesimprovement in welding and peeling resistance.

(ii) In the cutting tool of the present embodiment, for the α-Al₂O₃layer, the difference between the average particle diameter a of thefirst region and the average particle diameter b of the α-Al₂O₃particles in the second region (hereinafter, also referred to as“average particle diameter b of the second region”) is small, and thedifference between the average particle diameter b of the second regionand the average particle diameter c of the α-Al₂O₃ particles in thethird region (hereinafter, also referred to as “average particlediameter c of the third region”) is small. This inhibits interfaces fromoccurring between the first region and the second region and between thesecond region and the third region due to the difference in the particlediameters. The α-Al₂O₃ layer has a large adhesion between the firstregion and the second region and between the second region and the thirdregion, due to the interfaces, which are the starting point of cracks,being inhibited from occurring, and the cutting tool has therebyexcellent fracture resistance.

(iii) The cutting tool of the present embodiment has the particlediameter of the α-Al₂O₃ particles gradually increasing from the basematerial side toward the tool surface side in the region of on the basematerial side of the α-Al₂O₃ layer. Therefore, the crack propagationdistance from the tool surface is long, and cracks on the base materialside of the α-Al₂O₃ layer are inhibited from extending. Accordingly, thecutting tool has excellent fracture resistance.

(iv) In the cutting tool of the present embodiment, the average particlediameter c of the third region of the α-Al₂O₃ layer is 0.10 μm or more,and cracks are thereby inhibited from extending from the tool surface,so that the cutting tool has excellent fracture resistance. The averageparticle diameter c is 0.30 μm or less, and the cutting tool thereby hasexcellent wear resistance.

(v) In the cutting tool of the present embodiment, the ratio b/a betweenthe average particle diameter b of the first region of the α-Al₂O₃ layerand the average particle diameter a of the second region of the α-Al₂O₃layer is 1.5 or more, that is, the average particle diameter b is largerthan the average particle diameter a, so that cracks do not easilyextend in the first region and the second region in the direction of thethickness of the coating and the cutting tool has thereby excellentfracture resistance. The ratio b/a is 5.0 or less, that is, thedifference between the average particle diameter a and the averageparticle diameter b is small. This inhibits an interface from occurringbetween the first region and the second region due to the difference inthe particle diameters. The α-Al₂O₃ layer has a large adhesion betweenthe first region and the second region, due to the interfaces, which arethe starting point of cracks, being inhibited from occurring, and thecutting tool has thereby excellent fracture resistance.

(vi) As described in (i) to (v) above, the cutting tool of the presentembodiment has excellent fracture resistance and wear resistance, andcan have a long tool life even in high-efficiency machining ofhigh-hardness steel.

<Configuration of Cutting Tool>

As shown in FIG. 1, a cutting tool 1 of the present embodiment comprisesa base material 10 and a coating 15 arranged on base material 10,wherein coating 15 comprises an α-Al₂O₃ layer 11. Coating 15 preferablycoats at least a part of the portion, involved in cutting, of a rakeface of the base material, preferably coats at least a part of theportion, involved in cutting, of the base material, and further morepreferably coats the entire surface of the base material. The portion,involved in cutting, of the base material means a region, on the surfaceof the base material, which is at the distance within 1.5 mm from theridge line of the cutting edge. Even if a part of the base material isnot coated with this coating or the configuration of the coating ispartly different, it will not deviate from the scope of the presentdisclosure.

<Applications of Cutting Tool>

Examples of the cutting tools of the present disclosure can include adrill, an end mill (such as a ball end mill), a cutting-edge-replaceablecutting tip for a drill, a cutting-edge-replaceable cutting tip for anend mill, a cutting-edge-replaceable cutting tip for milling acutting-edge-replaceable cutting tip for turning, a metal saw, a gearcutting tool, a reamer and a tap.

<Base Material>

Base material 10 comprises a rake face and a flank face, and any basematerial of this type conventionally known may be used. For example, thebase material is preferably any one of cemented carbides (for example,WC-based cemented carbides such as WC—Co-based cemented carbides; thecemented carbides can contain a carbonitride of Ti, Ta, Nb or the like),cermets (those that contain TiC, TiN, TiCN or the like as a maincomponent), high-speed steels, ceramics (such as titanium carbide,silicon carbide, silicon nitride, aluminum nitride and aluminum oxide),cubic boron nitride sintered materials and diamond sintered materials.

Among these various base materials, it is preferable to select cementedcarbides (particularly WC-based cemented carbides) or cermets(particularly TiCN-based cermets). These base materials have anexcellent balance of hardness and strength at a high temperature, andhave excellent properties as base materials for cutting tools for theabove-described applications. When a WC-based cemented carbide is usedas a base material, it may contain a free carbon and an abnormal layersuch as that referred to as an η phase or an c phase in its structure.

The surface of the base material may also be modified. For example, inthe case of a cemented carbide, it may have a n-free layer formed on thesurface thereof, and in the case of a cermet, it may have a hardenedlayer formed on the surface. The base material exhibits the desiredeffect even if its surface is modified.

When the cutting tool is a cutting-edge-replaceable cutting tip, thebase material may or may not have a tip breaker. The ridge line of thecutting edge used may have any shape such as a sharp edge shape (onehaving a ridge where a rake face and a flank face intersect), a honingshape (one having a rounded sharp edge), a negative land shape (achamfered one), or a combination of a honing shape and a negative landshape.

<Coating>

The coating comprises an α-Al₂O₃ layer. For example, the coating maycomprise a plurality of layers comprising one or more α-Al₂O₃ layers andthe other layer(s).

Coating 15 may comprise the other layer(s) in addition to α-Al₂O₃ layer11.

For example, as shown in a cutting tool 21 in FIG. 2, a coating 25 mayfurther comprise an underlayer 12 arranged between base material 10 andα-Al₂O₃ layer 11.

As shown in a cutting tool 31 in FIG. 3, a coating 35 may comprise asurface layer 13 arranged on α-Al₂O₃ layer 11 in addition to underlayer12.

As shown in a cutting tool 41 in FIG. 4, a coating 45 may furthercomprise an interlayer 14 arranged between underlayer 12 and α-Al₂O₃layer 11 in addition to underlayer 12 and surface layer 13. Details ofthe underlayer, the surface layer and the interlayer will be describedlater.

The average thickness of the entire coating arranged on the basematerial is preferably 3 μm or more and 30 μm or less. Such a coatingcan have excellent wear resistance and peeling resistance. The averagethickness of the coating is more preferably 5 μm or more and 25 μm orless and further preferably 8 μm or more and 20 μm or less.

The thickness of the coating described above is measured, for example,by obtaining a cross-sectional sample parallel to the normal directionof the surface of the base material and observing this sample with ascanning transmission electron microscope (STEM). Examples of thescanning transmission electron microscope include JEM-2100F (trade name)manufactured by JEOL Ltd.

As used herein, the term “thickness” means an average thickness.Specifically, the observation magnification for the cross-sectionalsample is set to 5000 times, and a rectangular measured field of viewthat is (30 μm in the direction parallel to the surface of the basematerial)×(distance including the entire thickness of the coating) isset in the electron microscopic image. The thickness size is measured at10 points in the field of view, and the average value thereof is definedas “thickness”. The thickness and average thickness of the underlayer,the interlayer and the surface layer described below are also measuredand calculated in the same manner.

It was confirmed that similar results could be obtained, even when aplurality of measured fields of view covering a coating on the rake faceor a coating on the flank face were arbitrarily selected for the samespecimen, the above measurement is carried out in the measured fields ofview and the above average thickness is calculated.

<α-Al₂O₃ Layer>

(Configuration of α-Al₂O₃ Layer)

In the present embodiment, the α-Al₂O₃ layer is composed of a pluralityof α-Al₂O₃ (aluminum oxide having an α-type crystal structure)particles. That is, the α-Al₂O₃ layer is composed of polycrystallineα-Al₂O₃. The α-Al₂O₃ layer may contain unavoidable impurities and thelike as long as they exhibit the effects of the present embodiment. Thatis, the α-Al₂O₃ layer may contain other components as long as they donot impair the effects of the present disclosure.

In the present embodiment, α-Al₂O₃ layer 11 arranged on the rake face ofbase material 10 comprises a first region A1, a second region A2 and athird region A3. First region A1, second region A2 and third region A3are defined herein as the following regions.

First region A1 is a region sandwiched between interface P1 on the sideof base material 10 of α-Al₂O₃ layer 11 and virtual surface S1 that islocated at a distance of 0.5 μm from interface P1 toward the side ofsurface P2 of coating 15, wherein interface P1 is included in firstregion A1 and virtual surface S1 is not included in first region A1.

Second region A2 is a region sandwiched between virtual surface S1 andvirtual surface S2 that is located at a distance of 1.0 μm from virtualsurface S1 toward the side of surface P2 of coating 15, wherein virtualsurface S1 and virtual surface S2 are included in second region A2.

When α-Al₂O₃ layer 11 is arranged on the outermost surface of thecoating (for example, as shown in FIGS. 1 and 2), third region A3 is aregion sandwiched between surface P2 of α-Al₂O₃ layer 11 and virtualsurface S3 that is located at a distance of 1.0 μm from surface P2toward the base material side, wherein surface P2 and virtual surface S3are included in third region A3.

When another layer (surface layer) is arranged on α-Al₂O₃ layer 11 (forexample, as shown in FIGS. 3 and 4), third region A3 is a regionsandwiched between interface P3 on the surface side of the coating ofthe α-Al₂O₃ layer 11 and virtual surface S3 that is located at adistance of 1.0 μm from interface P3 toward the side of base material10, wherein interface P3 and virtual surface S3 are included in thirdregion A3.

The second region and the third region may be in contact with eachother. Another region may be further arranged between the second regionand the third region, wherein another region is a region sandwichedbetween virtual surface S2 and virtual surface S3.

(Average Particle Diameter of α-Al₂O₃Particles)

In the present embodiment, the average particle diameter a of theα-Al₂O₃ particles in the first region is 0.10 μm or more and 0.30 μm orless; the average particle diameter b of the α-Al₂O₃ particles in thesecond region is 0.30 μm or more and 0.50 μm or less; the averageparticle diameter c of the α-Al₂O₃ particles in the third region is 0.10μm or more and 0.30 μm or less; and the ratio b/a between the averageparticle diameter b and the average particle diameter a is 1.5 or moreand 5.0 or less.

When the average particle diameter a of the α-Al₂O₃ particles in thefirst region is 0.10 μm or more and 0.30 μm or less, the α-Al₂O₃ layerhas a large adhesion to the layer in contact with the base material sideof the α-Al₂O₃ layer or to the base material in contact with the α-Al₂O₃layer. Therefore, at the time of cutting, the cutting tool does noteasily cause crack extension starting from the interface between theα-Al₂O₃ layer and the underlayer or the base material and has therebyexcellent fracture resistance. The average particle diameter a ispreferably 0.12 μm or more and 0.28 μm or less, more preferably 0.14 μmor more and 0.26 μm or less and further preferably 0.16 μm or more and0.24 μm or less from the viewpoint of improving adhesion and fractureresistance.

When the average particle diameter b of the α-Al₂O₃ particles in thesecond region is 0.30 μm or more, cracks can be inhibited from extendingfrom the tool surface, resulting in improvement in fracture resistance.On the other hand, when the average particle diameter b is 0.50 μm orless, the difference between the average particle diameter b and theaverage particle diameter a of the α-Al₂O₃ particles in the first regionis small, and an interface is thereby inhibited from occurring betweenthe first region and the second region due to the difference in theparticle diameters. Therefore, the cutting tool does not easily causecrack extension starting from the interface and is inhibited from areduction in the adhesion between the first region and the secondregion, so that it can have thereby excellent fracture resistance. Inaddition, the difference between the average particle diameter b of theα-Al₂O₃ particles in the second region and the average particle diameterc of the α-Al₂O₃ particles in the third region is small, and aninterface is inhibited from occurring between the second region and thethird region due to the difference in the particle diameters. Therefore,the cutting tool does not easily cause crack extension starting from theinterface and is inhibited from a reduction in the adhesion between thesecond region and the third region, so that it can have therebyexcellent fracture resistance. The average particle diameter b ispreferably 0.32 μm or more and 0.48 μm or less, more preferably 0.34 μmor more and 0.46 μm or less and further preferably 0.36 μm or more and0.44 μm or less from the viewpoint of improving adhesion and fractureresistance.

The average particle diameter c of the α-Al₂O₃ particles in the thirdregion is 0.10 μm or more, and cracks are thereby inhibited fromextending from the tool surface, so that the cutting tool can haveexcellent fracture resistance. The average particle diameter c is 0.30μm or less, and the cutting tool can thereby have excellent wearresistance. The average particle diameter c is preferably 0.12 μm ormore and 0.28 μm or less, more preferably 0.14 μm or more and 0.26 μm orless and further preferably 0.16 μm or more and 0.24 μm or less.

The ratio b/a between the average particle diameter b and the averageparticle diameter a is 1.5 or more and 5.0 or less. When the ratio b/ais 1.5 or more, the average particle diameter b is larger than theaverage particle diameter a, and cracks do not easily extend in thefirst region and the second region in the direction of the thickness ofthe coating, so that the cutting tool has excellent fracture resistance.On the other hand, when the ratio b/a is 5 or less, the differencebetween the average particle diameter a and the average particlediameter b is small, adhesion between the first region and the secondregion is thereby improved, so that cracks are inhibited from occurringin the first region and the second region. Accordingly, the cutting toolhas excellent fracture resistance.

In the present specification, the average particle diameter a, theaverage particle diameter b, and the average particle diameter c aremeasured according to the following procedures (A1) to (A8).

(A1) A cutting tool is cut out with a diamond wire along the normal lineof a rake face of a base material to expos a cross section of an α-Al₂O₃layer. The exposed cross section is subjected to Ar ion milling to makethe cross section in a mirror surface state. The conditions for the ionmilling are as follows.

Accelerating voltage: 6 kV

Irradiation angle: 0° from the linear direction parallel to thethickness direction of the α-Al₂O₃ layer in the cross section of theα-Al₂O₃ layer

Irradiation time: 6 hours

(A2) The cross section in a mirror surface state is observed with afield-emission scanning electron microscope (EF-SEM) at a magnificationof 5000 times to obtain a backscattered electron image (EBSD). FIG. 5 isa diagram schematically showing an example of an EBSD.

(A3) In the above EBSD, a region where a difference D1, of the distancesalong the normal direction of the rake face, between a bottom portion B1and a peak portion T1 of the irregularities of interface P1 on the basematerial side of the α-Al₂O₃ layer is 0.5 μm or less is identified, andthe measurement range is set so that it includes the region. Themeasurement range is a rectangle that is (the horizontal direction (thedirection parallel to the rake face): 30 μm)×(the vertical direction(normal direction of the rake face): length including the entirecoating).

(A4) A reference line LS1 is set at a position intermediate betweenbottom portion B1 and peak portion T1 of interface P1 within the abovemeasurement range.

(A5) The horizontal particle diameters of the α-Al₂O₃ particles aremeasured on a line L1 0.2 μm away from reference line LS1 toward thedirection of the surface of the cutting tool. The particle diameters ofall the α-Al₂O₃ particles in the measurement range are measured, and theaverage value thereof is taken as the average particle diameter a of theα-Al₂O₃ particles in the first region.

(A6) The horizontal particle diameters of the α-Al₂O₃ particles aremeasured on a line L2 1.1 μm away from reference line LS1 toward thedirection of the surface of the cutting tool. The particle diameters ofall the α-Al₂O₃ particles in the measurement range are measured, and theaverage value thereof is taken as the average particle diameter b of theα-Al₂O₃ particles in the second region.

(A7) Within the above measurement range, when the α-Al₂O₃ layer isarranged on the outermost surface of the coating, the horizontalparticle diameters of the α-Al₂O₃ particles are measured on a line L30.6 μm away from surface P2 of the α-Al₂O₃ layer toward the direction ofthe base material, or when a surface layer is arranged on the α-Al₂O₃layer, the horizontal particle diameters of the α-Al₂O₃ particles aremeasured on line L3 0.6 μm away from interface P3 (an interface betweenthe α-Al₂O₃ layer and the surface layer) on the surface side of thecoating of the α-Al₂O₃ layer toward the direction of the base material.The particle diameters of all the α-Al₂O₃ particles in the measurementrange are measured, and the average value thereof is taken as theaverage particle diameter c of the α-Al₂O₃ particles in the thirdregion. When surface P2 and interface P3 have irregularities, line L3 isset at a distance of 0.6 μm away from a line that passes through thebottom portion located closest to the base material side in themeasurement range and is parallel to reference line LS1 toward thedirection of the base material.

In the above (A5), when the difference between bottom portion B1 andpeak portion T1 of the interface is large (for example, 0.5 μm) and lineL1 exists inside the base material as shown in FIG. 6, the particlediameters of the α-Al₂O₃ particles are measured not on line L1 insidethe base material (for example, in a region represented by X in FIG. 6)but only for the inside of the α-Al₂O₃ layer. The average particlediameter a is then calculated.

In setting line L1, the present inventors set lines La1 to Ld1 passingthrough positions at intervals of 0.1 μm within a range that is at adistance of 0.1 μm or more and less than 0.5 μm from reference line LS1along the normal direction of the rake face in the first region as shownin FIG. 7; measured the particle diameters of all the α-Al₂O₃ particlesin the measurement range on each line and on interface S1; andcalculated the average value thereof. As a result, it was confirmed thatwhen the average particle diameter on a line Lb1 corresponding to lineL1 was 0.10 μm or more and 0.30 μm or less, the average particlediameters on lines La1 to Ld1 and interface S1 were also 0.10 μm or moreand 0.30 μm or less. This is presumed to be because nucleation in theinitial stage is greatly affected by the orientation and irregularitiesof the underlayer and Al₂O₃ crystals thereby grow not in a columnarshape (or in a shape in which the cross-sectional particle diameterincreases toward the surface) but in a granular shape (they are grownevenly to some extent perpendicularly and parallel to the interface).

It was confirmed that the similar results could be obtained even ifdifferent measurement ranges were arbitrarily selected for the samecutting tool and the above measurement was carried out in themeasurement range. In addition, it was confirmed that the similarresults could be obtained even if different measurement ranges werearbitrarily selected for the different cutting tool and the abovemeasurement was carried out in the measurement range. Accordingly, theaverage particle diameter on line L1 of 0.10 μm or more and 0.30 μm orless means the average particle diameter a of the α-Al₂O₃ particles inthe first region of 0.10 μm or more and 0.30 μm or less.

In setting line L2, the present inventors set lines La2 to Lf2 passingthrough positions at intervals of 0.2 μm within a range that is at adistance of 0.5 μm or more and 1.5 μm or less from reference line LS1along the normal direction of the rake face in the second region asshown in FIG. 7; measured the particle diameters of all the α-Al₂O₃particles in the measurement range on each line; and calculated theaverage value thereof. As a result, it was confirmed that when theaverage particle diameter on a line Ld2 corresponding to line L2 was0.30 μm or more and 0.50 μm or less, the average particle diameters onlines La2 to Lf2 were also 0.30 μm or more and 0.50 μm or less. This ispresumed to be for the following reasons. The second region is atransition region from nucleation to crystal growth. In the firstregion, nucleation occurred under the influence of the orientation,irregularities and the like of the base material in addition to the gasconditions, but in the second region, the influence of gas conditionspredominates and the nucleus different (in orientation, shape and thelike) from that in the first region predominates. It is presumed thatthe total number of particles does not change significantly and thechange in the particle diameter is not large, because the crystalsproduced by nucleation are weeded out while stable nuclei are generatedunder new gas conditions. In addition, in the present disclosure, thegas conditions during forming the first region and the second region areadjusted to gently transition between weeding-out and nucleation ofcrystals, thereby extending the second region in the thickness directionand maintaining the particle diameter.

It was confirmed that the similar results could be obtained even ifdifferent measurement ranges were arbitrarily selected for the samecutting tool and the above measurement was carried out in themeasurement range. In addition, it was confirmed that the similarresults could be obtained even if different measurement ranges werearbitrarily selected for the different cutting tool and the abovemeasurement was carried out in the measurement range. Accordingly, theaverage particle diameter on line L2 of 0.30 μm or more and 0.50 μm orless means the average particle diameter b of the α-Al₂O₃ particles inthe second region of 0.30 μm or more and 0.50 μm or less.

In setting line L3, the present inventors set lines La3 to Lf3 passingthrough positions at intervals of 0.2 μm within a range that is at adistance of 0 μm or more and 1.0 μm or less from surface P2 of theα-Al₂O₃ layer or interface P3 on the surface side of the coating of theα-Al₂O₃ layer along the normal direction of the rake face in the thirdregion as shown in FIG. 7; measured the particle diameters of all theα-Al₂O₃ particles in the measurement range on each line; and calculatedthe average value thereof. As a result, it was confirmed that when theaverage particle diameter on a line Ld3 corresponding to line L3 was0.10 μm or more and 0.30 μm or less, the average particle diameters onlines La3 to Lf3 were also 0.10 μm or more and 0.30 μm or less. This ispresumed to be because the third region is completely a crystal growthregion and the change in the number of crystals is small.

It was confirmed that the similar results could be obtained even ifdifferent measurement ranges were arbitrarily selected for the samecutting tool and the above measurement was carried out in themeasurement range. In addition, it was confirmed that the similarresults could be obtained even if different measurement ranges werearbitrarily selected for the different cutting tool and the abovemeasurement was carried out in the measurement range. Accordingly, theaverage particle diameter on line L3 of 0.10 μm or more and 0.30 μm orless means the average particle diameter c of the α-Al₂O₃ particles inthe third region of 0.10 μm or more and 0.30 μm or less.

It is confirmed in the cutting tool that when the average particlediameter a of the α-Al₂O₃ particles in the first region is 0.10 μm ormore and 0.30 μm or less; the average particle diameter b of the α-Al₂O₃particles in the second region is 0.30 μm or more and 0.50 μm or less;the average particle diameter c of the α-Al₂O₃ particles in the thirdregion is 0.10 μm or more and 0.30 μm or less; and the ratio b/a betweenb and a is 1.5 or more and 5.0 or less, the effect is not influencedeven if the distance between line L2 and line L3 changes.

Based on the above, the cutting tool of the present embodiment can alsobe expressed as follows.

The cutting tool of the present disclosure is:

a cutting tool comprising a base material and a coating arranged on thebase material;

wherein:

the coating comprises an α-Al₂O₃ layer; and

the α-Al₂O₃ layer is composed of a plurality of α-Al₂O₃ particles;

wherein:

in the cross section along the normal line of the surface of thecoating, the average particle diameter of the α-Al₂O₃ particles, on lineL1 that is at the distance of 0.2 μm from reference line LS1 based onthe interface between the base material and the α-Al₂O₃ layer toward theα-Al₂O₃ layer side, is 0.10 μm or more and 0.30 μm or less;

the average particle diameter of the α-Al₂O₃ particles, on line L2 thatis at the distance of 1.1 μm from reference line LS1 toward the α-Al₂O₃layer side, is 0.30 μm or more and 0.50 μm or less;

the average particle diameter of the α-Al₂O₃ particles, on line L3 thatis at the distance of 0.6 μm from surface P2 of the α-Al₂O₃ layer orfrom interface P3 on the surface side of the coating of the α-Al₂O₃layer toward the α-Al₂O₃ layer side, is 0.10 μm or more and 0.30 μm orless; and

the ratio b/a between b and a is 1.5 or more and 5.0 or less.

(b/a)

In the cutting tool of the present embodiment, the ratio b/a between theaverage particle diameter b of the α-Al₂O₃ layer in the first region andthe average particle diameter a of the α-Al₂O₃ layer in the secondregion is 1.5 or more and 5.0 or less. The ratio b/a is 1.5 or more,that is, the average particle diameter b is larger than the averageparticle diameter a, so that the cutting tool does not easily extendcracks in the first region and the second region in the direction of itsthickness and the cutting tool thereby has excellent fractureresistance. On the other hand, the ratio b/a is 5 or less, that is, thedifference between the average particle diameter a and the averageparticle diameter b is small, so that adhesion between the first regionand the second region is improved and cracks are thereby inhibited fromoccurring in the first region and the second region. Accordingly, thecutting tool has excellent fracture resistance.

From the viewpoint of improving the adhesion between the first regionand the second region and improving the fracture resistance, the ratiob/a is preferably 1.5 or more and 2.5 or less, more preferably 1.7 ormore and 2.3 or less and further preferably 1.9 or more and 2.1 or less.

(Orientation Index)

In the present disclosure, the α-Al₂O₃ layer preferably has a TC (0 012) of 3 or more in an orientation index TC (hkl) represented by thefollowing expression (1). The α-Al₂O₃ layer having such a TC (0 0 12)can have excellent wear resistance. Accordingly, the cutting tool canhave a long tool life.

$\begin{matrix}\left\lbrack {{Expression}1} \right\rbrack &  \\{{{TC}({hkl})} = {\frac{I({hkl})}{I_{0}({hkl})}\left\{ {\frac{1}{n}{\sum\limits_{1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\}^{- 1}}} & (1)\end{matrix}$

In the expression (1), I (hkl) represents the X-ray diffractionintensity on the reflection plane (hkl), and I₀ (hkl) represents thestandard intensity according to the PDF card No. 00-010-0173 of ICDD. Inthe expression (1), n represents the number of reflections used in thecalculation and is 8 in the present embodiment. The planes (hkl) usedfor reflection are (012), (104), (110), (0 0 12), (113), (024), (116)and (300).

ICDD (registered trademark) is an abbreviation for International Centrefor Diffraction Data. PDF (registered trademark) is an abbreviation forPower Diffraction File.

TC (0 0 12) of the α-Al₂O₃ layer of the present embodiment can berepresented by the following expression (2).

$\begin{matrix}\left\lbrack {{Expression}2} \right\rbrack &  \\{{{TC}\left( {0012} \right)} = {\frac{I\left( {0012} \right)}{I_{0}\left( {0012} \right)}\left\{ {\frac{1}{8}{\sum\limits_{1}^{8}\frac{I({hkl})}{I_{0}({hkl})}}} \right\}^{- 1}}} & (2)\end{matrix}$

Accordingly, “TC (0 0 12) of 3 or more in the orientation index TC(hkl)” means that the numerical value determined by the above expression(2) obtained by substituting TC (0 0 12) into the above expression (1)is 3 or more.

The value of TC (0 0 12) is more preferably 4 or more and furtherpreferably 5 or more. The larger the value of TC (0 0 12) is, the moreeffectively the wear resistance can be improved. The upper limit of thevalue of TC (0 0 12) is not limited, but since eight reflection planesare used in the calculation, it may be set to 8 or less. The value of TC(0 0 12) can be set to 3 or more and 8 or less, 4 or more and 8 or less,or 5 or more and 8 or less.

In the present disclosure, the α-Al₂O₃ layer preferably has a TC (110)of 2 or more in an orientation index TC (hkl) represented by the aboveexpression (1). The α-Al₂O₃ layer having such a TC (110) can haveexcellent fracture resistance. Accordingly, the cutting tool can have along tool life.

TC (110) of the α-Al₂O₃ layer of the present embodiment can berepresented by the following expression (3).

$\begin{matrix}\left\lbrack {{Expression}3} \right\rbrack &  \\{{{TC}(110)} = {\frac{I(110)}{I_{0}(110)}\left\{ {\frac{1}{8}{\sum\limits_{1}^{8}\frac{I({hkl})}{I_{0}({hkl})}}} \right\}^{- 1}}} & (3)\end{matrix}$

Accordingly, “TC (110) of 2 or more in the orientation index TC (hkl)”means that the numerical value determined by the above expression (3)obtained by substituting TC (110) into the above expression (1) is 2 ormore.

The value of TC (110) is more preferably 2.5 or more and furtherpreferably 3 or more. The larger the value of TC (110) (0 0 12) is, themore effectively the fracture resistance can be improved. The upperlimit of the value of TC (110) is not limited, but since eightreflection planes are used in the calculation, it may be set to 8 orless. The value of TC (110) can be set to 2 or more and 8 or less, 2.5or more and 8 or less, or 3 or more and 8 or less.

The TC (hkl) measurement as described above can be performed by analysiswith an X-ray diffractometer. TC (hkl) can be measured, for example,using SmartL b/a (registered trademark) (scan speed: 21.7°/min; step:0.01°; scan range: 15 to) 140° manufactured by Rigaku Corporation underthe following conditions. In the present embodiment, the measurementresults of TC (hkl) with the X-ray diffractometer are referred to as“XRD results”.

Characteristic X-ray: Cu-Kα

Tube voltage: 45 kV

Tube current: 200 mA

Filter: multi-layer mirror

Optical system: concentration method

X-Ray diffraction method: 0-20 method

When using the X-ray diffractometer, the flank face of the cutting toolis irradiated with X-rays. Usually, the rake face has irregularitiesformed thereon, whereas the flank face has a flat surface. Therefore, itis preferable to irradiate the flank face with X-rays in order toeliminate disturbance factors. The flank face is irradiated with X-raysparticularly on an area that extends in a range of about 2 to 4 mm froma ridge line of a cutting edge. This results in a high reproducibility.In the present embodiment, the values of TC (hkl) of the α-Al₂O₃ layeron the flank face of the base material are the same as the values of TC(hkl) of the α-Al₂O₃ layer on the rake face of the base material.

It was confirmed that the similar results could be obtained even if aplurality of measurement areas were arbitrarily selected for the samespecimen and the above measurement was carried out for each of themeasurement ranges.

(Thickness)

The average thickness of the α-Al₂O₃ layer is preferably 3 μm or moreand 15 μm or less. This can result in both excellent wear resistance andfracture resistance at the same time. The lower limit of the averagethickness of the α-Al₂O₃ layer is preferably 3 μm or more, morepreferably 4 μm or more and further more preferably 5 μm or more, fromthe viewpoint of improving wear resistance. If the average thickness ofthe α-Al₂O₃ layer is less than 3 μm, the thickness is insufficient, sothat the average particle diameter a, the average particle diameter b,the average particle diameter c, and b/a of the α-Al₂O₃ layer describedabove cannot be defined.

The upper limit of the average thickness of the α-Al₂O₃ layer ispreferably 15 μm or less, preferably 10 μm or less, more preferably 9 μmor less and further more preferably 8 μm or more, from the viewpoint ofimproving fracture resistance. The average thickness of the α-Al₂O₃layer is preferably 3 μm or more and 10 μm or less, more preferably 4 μmor more and 9 μm or less and further preferably 5 μm or more and 8 μm orless.

As described above, the thickness of the α-Al₂O₃ layer can be checked byobserving a cross-sectional sample with a scanning transmission electronmicroscope (STEM) or the like. Then, the observation field of view isthe measurement range set in measuring the particle diameter of theα-Al₂O₃ particles as described above.

It was confirmed that similar results could be obtained, even if aplurality of measurement ranges covering a coating on the rake face or acoating on the flank face were arbitrarily selected for the samespecimen and the above measurement was carried out for each of themeasurement ranges.

<Other Layers>

The coating may comprise the other layers in addition to the α-Al₂O₃layer. As shown in FIGS. 2 to 4, examples of the other layers includeunderlayer 12, surface layer 13 and interlayer 14.

(Underlayer)

The underlayer is arranged between the base material and the α-Al₂O₃layer. Examples of the underlayer include a TiN layer. The TiN layerpreferably has an average thickness of 0.1 μm or more and 20 μm or less.This enables the coating to have excellent wear resistance and fractureresistance.

(Surface Layer)

The surface layer preferably contains, for example, any of a carbide,nitride and boride of Ti (titanium) as a main component. The surfacelayer is a layer arranged on the outermost surface side of the coating.However, the surface layer may not be formed at a ridge line of acutting edge. The surface layer is arranged, for example, directly abovethe α-Al₂O₃ layer.

The expression “contain any of a carbide, nitride and boride of Ti as amain component” means that 90% by mass or more of any of a carbide,nitride and boride of Ti is contained. It also means that the surfacelayer preferably comprises any of a carbide, nitride and boride of Tiexcept for unavoidable impurities.

Among carbide, nitride and carbonitride of Ti, a nitride of Ti (that is,a compound represented by TiN) is particularly preferably used as a maincomponent constituting a surface layer. Of these compounds, TiN exhibitsthe clearest color (exhibits a gold color). Therefore, it has anadvantage that it is easy to identify the corners of the cutting tipthat have been already used (identify the used area). The surface layerpreferably comprises a TiN layer.

The surface layer preferably has an average thickness of 0.05 μm or moreand 1 μm or less. This results in improved adhesion between the surfacelayer and a layer adjacent thereto. The upper limit of the averagethickness of the surface layer can be 0.8 μm or less or 0.6 μm or less.The lower limit of the average thickness can be 0.1 μm or more or 0.2 μmor more.

<Interlayer>

The interlayer is arranged between the underlayer and the α-Al₂O₃ layer.Examples of the interlayer include a TiCN layer and a TiCNO layer. TheTiCN layer and the TiCNO layer can impart more suitable wear resistanceto the coating due to their excellent wear resistance. The interlayerpreferably has an average thickness of 1 μm or more and 20 μm or less.When the interlayer is formed from two or more layers, the averagethickness of the interlayer means the average of the total thickness ofthe two or more layers.

Embodiment 2: Manufacturing Method of Cutting Tool

The cutting tool of Embodiment 1 can be manufactured by forming acoating on a base material by the chemical vapor deposition (CVD)method. When the other layers other than the α-Al₂O₃ layer is formed inthe coating, each of the layers can be formed using a chemical vapordeposition device under the conditions conventionally known. On theother hand, the α-Al₂O₃ layer can be formed, for example, as follows.The cutting tool of Embodiment 1 is not limited to that manufactured bythe following manufacturing method, and may be manufactured by the othermanufacturing method.

The film deposition conditions for the α-Al₂O₃ layer can be, forexample, a temperature of 950 to 1050° C., a pressure of 10 to 50 hPaand a gas flow rate (total gas flow rate) of 50 to 100 L/min. The “totalgas flow rate” refers to the total volume flow rate of the gasintroduced into a CVD furnace per unit time, with a gas in the normalstate (0° C., 1 atm) as an ideal gas.

Raw material gases used are AlCl₃, HCl, CO₂, H₂S and Hz. The proportionof HCl comprised in the raw material gases is varied depending on thethickness of the formed α-Al₂O₃ layer, from the start of the filmdeposition. Specifically, it is varied as follows.

From the start of film deposition until the thickness of the α-Al₂O₃layer is less than 0.5 μm, the proportions of the raw material gases aresuch that: HCl is 7.5% by volume or more and 9% by volume or less; AlCl₃is 2% by volume or more and 5% by volume or less; CO₂ is 0.1% by volumeor more and 6% by volume or less; H₂S is 0.1% by volume or more and 1%by volume or less; and Hz is the balance in % by volume, based on thetotal of the raw material gases of 100% by volume. The first region isformed in such a manner.

Subsequently, until the thickness of the α-Al₂O₃ layer is 0.5 μm or moreand 1.5 μm or less, the proportions of the raw material gases are setsuch that: HCl is 6% by volume or more and less than 7.5% by volume; theamount of Hz is increased by a decrement of HCl in the raw materialgases as compared with that during forming the first region; and theproportions of the other gases are the same as those during forming thefirst region. The second region is formed in such a manner.

Subsequently, until the thickness of the α-Al₂O₃ layer is a thickness1.0 μm smaller than the final thickness of the α-Al₂O₃ layer, theproportions of the raw material gases used are the same as those duringforming the second region.

Subsequently, from the thickness 1.0 μm smaller than the final thicknessof the α-Al₂O₃ layer to the surface of the α-Al₂O₃ layer, theproportions of the raw material gases are such that: HCl is 7.5% byvolume or more and less than 9.0% by volume; the amount of H₂ isdecreased by an increment of HCl in the raw material gases as comparedwith that that during forming the second region; and the proportions ofthe other gases are the same as those during forming the second region.The third region is formed in such a manner.

HCl has been conventionally used to inhibit α-Al₂O₃ from beingexcessively produced during film deposition and to inhibit α-Al₂O₃particles from being formed in the gas phase. When α-Al₂O₃ particles areformed in the gas phase, the α-Al₂O₃ layer is not easily formed on thebase material. On the other hand, it has been thought that a highproportion of HCl in the raw material gases will reduce the filmdeposition rate. Therefore, it has been common knowledge in the art thatthe proportion of HCl in the raw material gases should be minimized, andthere has been no technical idea to increase the proportion of HCl inthe raw material gases.

In contrast to the prior common knowledge in the art, in the presentembodiment, the proportion of HCl is varied in order to control theparticle diameters of the α-Al₂O₃ particles as described above. Theproportions of HCl in the raw material gases during forming the firstregion, the second region and the third region are higher than that ofHCl in the raw material gases conventionally used during forming anα-Al₂O₃ layer (for example, 2.8% by volume or more and less than 6% byvolume). This results in smaller average particle diameters of theα-Al₂O₃ particles in the first region, the second region and the thirdregion. This is a finding novelly found by the present inventors. Thepresent inventors have completed the cutting tool of the presentembodiments, based on this novel finding.

[Additional Description 1]

The cutting tool of the present disclosure is:

a cutting tool comprising a base material and a coating arranged on thebase material;

wherein:

the coating comprises an α-Al₂O₃ layer; and

the α-Al₂O₃ layer is composed of a plurality of α-Al₂O₃ particles;

wherein:

in the cross section along the normal line of the surface of thecoating,

the average particle diameter of the α-Al₂O₃ particles, on line L1 thatis at the distance of 0.2 μm from reference line LS1 based on theinterface between the base material and the α-Al₂O₃ layer toward theα-Al₂O₃ layer side, is 0.10 μm or more and 0.30 μm or less;

the average particle diameter of the α-Al₂O₃ particles, on line L2 thatis at the distance of 1.1 μm from reference line LS1 toward the α-Al₂O₃layer side, is 0.30 μm or more and 0.50 μm or less;

-   -   the average particle diameter of the α-Al₂O₃ particles, on line        L3 that is at the distance of 0.6 μm from surface P2 of the        α-Al₂O₃ layer or from interface P3 on the surface side of the        coating of the α-Al₂O₃ layer toward the α-Al₂O₃ layer side, is        0.10 μm or more and 0.30 μm or less; and

the ratio b/a between b and a is 1.5 or more and 5.0 or less.

EXAMPLES

The present embodiments will be more specifically described withreference to Examples. However, the present embodiments are not limitedby these Examples.

[Specimens 1 to 28 and Specimens 1-1 to 1-9]

The raw material powders having the formula composition shown in Table 1were uniformly mixed, pressure molded into a predetermined shapefollowed by sintering at 1300 to 1500° C. for one to two hours to obtaina base material made of a cemented carbide (shape: model number:CNMG120408N-UX (manufactured by Sumitomo Electric Hardmetal Corp.)). InTable 1, “Balance” indicates that WC comprises the remainder of theformula composition (% by mass).

[Table 1]

TABLE 1 Formula composition (% by mass) TaC NbC Co WC 2.0 1.0 10.0Balance

<Formation of Coating>

A coating was formed on the surface of the base material obtained aboveto manufacture a cutting tool. Specifically, the base material was setin a chemical vapor deposition device, and a coating was formed on thebase material by a chemical vapor deposition method. The configurationof the coating of each of the specimens is as shown in Table 2.

[Table 2]

TABLE 2 TiN TiCN TiCNO TiN layer Specimen layer layer layer α-Al₂O₃(Surface No. (Underlayer) (Interlayer) (Interlayer) layer layer) 1 YesYes Yes Yes Yes 2 Yes Yes Yes Yes Yes 3 Yes Yes Yes Yes Yes 4 Yes YesYes Yes Yes 5 Yes Yes Yes Yes Yes 6 Yes Yes Yes Yes Yes 7 Yes Yes YesYes Yes 8 Yes Yes Yes Yes Yes 9 Yes Yes Yes Yes Yes 10 Yes Yes Yes YesYes 11 Yes Yes Yes Yes Yes 12 Yes Yes Yes Yes Yes 13 Yes Yes Yes Yes Yes14 Yes Yes Yes Yes Yes 15 Yes Yes Yes Yes Yes 16 Yes Yes Yes Yes Yes 17Yes Yes Yes Yes Yes 18 Yes Yes Yes Yes Yes 19 Yes Yes Yes Yes Yes 20 YesYes Yes Yes Yes 21 No No No Yes Yes 22 Yes Yes Yes Yes No 23 No No NoYes No 24 Yes Yes Yes Yes Yes 25 Yes Yes Yes Yes Yes 26 Yes Yes Yes YesYes 27 Yes Yes Yes Yes Yes 28 Yes Yes Yes Yes Yes 1-1 Yes Yes Yes YesYes 1-2 Yes Yes Yes Yes Yes 1-3 Yes Yes Yes Yes Yes 1-4 Yes Yes Yes YesYes 1-5 Yes Yes Yes Yes Yes 1-6 Yes Yes Yes Yes Yes 1-7 No No No Yes Yes1-8 Yes Yes Yes Yes No 1-9 No No No Yes No

The following layers are formed on the base material in the orderlisted: a TiN layer (underlayer), a TiCN layer (interlayer), a TiCNOlayer (interlayer), an α-Al₂O₃ layer and a TiN layer (surface layer).The thickness of the TiN layer (underlayer) is 0.4 μm, the thickness ofthe TiCN layer (interlayer) is 6.5 μm, the thickness of the TiCNO layer(interlayer) is 0.7 μm, and the thickness of the TiN layer (surfacelayer) is 0.7 μm. In Table 1, “No” means that the layer in question isnot formed for the specimen in question.

Table 3 shows the film deposition conditions for the TiN layer(underlayer), the TiCN layer (interlayer), the TiCNO layer (interlayer)and the TiN layer (surface layer).

[Table 3]

TABLE 3 Film deposition Flow rate of raw conditions material gasesPressure Temperature (L/min) (hPa) (° C.) TiN layer TiCl₄:5, N₂:25,H₂:70 150 980 (Underlayer) TiCN layer TiCl₄:10, N₂:15, 100 850(Interlayer) CH₃CN:1.5, H₂:80 TiCNO layer TiCl₄:0.4, CH₄:2.5, CO:0.5,140 970 (Interlayer) N₂: 25, H₂:50 TiN layer TiCl₄:5, N₂:25, H₂:70 1501050 (Surface layer)

Table 4 shows the conditions for the film deposition of the α-Al₂O₃layer, the composition of the raw material gases and the averagethickness of the α-Al₂O₃ layer for each of the specimens. In Table 4,“Balance” means that H₂ gas comprises the remainder of the compositionof the raw material gases (% by volume). The conditions for forming theα-Al₂O₃ layer are a temperature of 1000° C., a pressure of 70 hPa and anintroduction rate of the raw material gases (total gas flow rate) of 60L/min, and a gas pipe for injecting the raw material gases was rotatedat 2 rpm while fixing the base material.

[Table 4]

TABLE 4 Film deposition conditions Total α-Al₂O₃ Composition of rawmaterial gases (% by volume) gas layer HCl flow Average Specimen FirstSecond Third Pressure Temperature rate thickness No. AlCl₃ region regionregion CO₂ H₂S H₂ (hPa) (° C.) (L/min) (μm) 1 2.2 8.3 6.7 8.3 3.0 0.6Balance 70 1000 60 8 2 2.2 8.3 6.7 8.3 3.0 0.2 Balance 70 1000 60 8 32.2 7.5 6.2 8.3 3.0 0.6 Balance 70 1000 60 8 4 2.2 7.3 6.1 8.3 3.0 0.6Balance 70 1000 60 8 5 2.2 9.0 7.0 8.3 3.0 0.6 Balance 70 1000 60 8 62.2 9.3 7.0 8.3 3.0 0.6 Balance 70 1000 60 8 7 2.2 8.3 6.0 8.3 3.0 0.6Balance 70 1000 60 8 8 2.2 8.3 5.5 8.3 3.0 0.6 Balance 70 1000 60 8 92.2 8.3 7.5 8.3 3.0 0.6 Balance 70 1000 60 8 10 2.2 8.6 7.9 8.3 3.0 0.6Balance 70 1000 60 8 11 2.2 8.6 7.9 8.3 3.0 0.2 Balance 70 1000 60 8 122.2 9.0 6.0 8.3 3.0 0.6 Balance 70 1000 60 8 13 2.2 8.0 7.0 8.3 3.0 0.6Balance 70 1000 60 8 14 2.2 7.9 7.3 8.3 3.0 0.6 Balance 70 1000 60 8 152.2 8.3 6.7 7.5 3.0 0.6 Balance 70 1000 60 8 16 2.2 8.3 6.7 6.7 3.0 0.6Balance 70 1000 60 8 17 2.2 8.3 6.7 9.0 3.0 0.6 Balance 70 1000 60 8 182.2 8.3 6.7 9.5 3.0 0.6 Balance 70 1000 60 8 19 2.2 8.3 6.7 8.3 3.0 0.6Balance 70 1000 60 3 20 2.2 8.3 6.7 8.3 3.0 0.6 Balance 70 1000 60 15 212.2 8.3 6.7 8.3 3.0 0.6 Balance 70 1000 60 8 22 2.2 8.3 6.7 8.3 3.0 0.6Balance 70 1000 60 8 23 2.2 8.3 6.7 8.3 3.0 0.6 Balance 70 1000 60 8 242.2 8.3 6.7 8.5 3.0 0.6 Balance 70 1000 60 8 25 2.2 8.3 6.7 8.0 3.0 0.6Balance 70 1000 60 8 26 2.2 8.5 6.0 8.3 3.0 0.6 Balance 70 1000 60 8 272.2 8.3 6.7 8.3 3.0 0.6 Balance 70 1000 60 18 28 2.2 8.3 6.7 8.3 3.0 0.5Balance 70 1000 60 8 1-1 2.2 6.7 4.5 3.5 3.0 0.6 Balance 70 1000 60 81-2 2.2 8.3 4.5 3.5 3.0 0.6 Balance 70 1000 60 8 1-3 2.2 6.7 4.5 3.5 3.00.2 Balance 70 1000 60 8 1-4 2.2 8.3 4.5 3.5 3.0 0.2 Balance 70 1000 608 1-5 2.2 8.3 4.5 3.5 3.0 0.6 Balance 70 1000 60 3 1-6 2.2 8.3 4.5 3.53.0 0.6 Balance 70 1000 60 15 1-7 2.2 8.3 4.5 3.5 3.0 0.6 Balance 701000 60 8 1-8 2.2 8.3 4.5 3.5 3.0 0.6 Balance 70 1000 60 8 1-9 2.2 8.34.5 3.5 3.0 0.6 Balance 70 1000 60 8

For example, the film deposition conditions of Specimen 1 are asfollows. From the start of film deposition until the thickness of theα-Al₂O₃ layer was 0.5 nm, the formula composition of the raw materialgases used was such that AlCl₃ was 2.2% by volume, HCl was 8.3% byvolume, CO₂ was 3.0% by volume and H₂S was 0.6% by volume with thebalance being Hz. The first region was formed in such a manner.

Subsequently, from the thickness of the α-Al₂O₃ layer above 0.5 μm untilthe thickness of the α-Al₂O₃ layer was a thickness 1 μm smaller than theaverage thickness (8 μm) of the α-Al₂O₃ layer (7 μm), the composition ofthe raw material gases having the same formula composition as thatduring forming the first region was used except that the proportion ofHCl in the raw material gases was 6.7% by volume and the proportion ofthe balance Hz was changed accordingly. The second region was formed insuch a manner.

Subsequently, from the thickness 1.0 μm smaller than the final thicknessof the α-Al₂O₃ layer to the surface of the α-Al₂O₃ layer, thecomposition of the raw material gases having the same formulascomposition as that during forming the second region was used exceptthat the proportion of HCl in the raw material gases was 8.3% by volumeand the proportion of the balance Hz was changed accordingly. The thirdregion was formed in such a manner.

<Evaluation of α-Al₂O₃ Layer>

For the α-Al₂O₃ layer of each of the specimens, the average particlediameter a of the first region, the average particle diameter b of thesecond region and the average particle diameter c of the third region,and TC (0 0 12) and TC (110) were measured.

These measurement methods are as shown in Embodiment 1, and they will bethereby not described repeatedly. The results are shown in the columns“Particle diameter a”, “Particle diameter b” and “Particle diameter c”,and “TC (0 0 12)” and “TC (110)” in Table 5.

Further, the value of b/a was calculated based on the average particlediameter a and the average particle diameter b. The results are shown inthe column “b/a” in Table 5.

[Table 5]

TABLE 5 α-Al₂O₃ layer Cutting Cutting Average Particle Particle Particleevaluation evaluation thick- diameter diameter diameter 1 2 Specimenness TC TC a b c Fracture Vb No. (μm) (0 0 12) (110) (μm) (μm) (μm) b/arate (%) (mm) 1 8 7.6 0.2 0.20 0.40 0.20 2.0 20 0.11 2 8 2.4 4.6 0.200.40 0.20 2.0 20 0.20 3 8 7.3 0.4 0.30 0.48 0.20 1.6 50 0.11 4 8 7.3 0.40.32 0.49 0.20 1.5 60 0.12 5 8 7.2 0.3 0.10 0.35 0.20 3.5 30 0.12 6 87.4 0.2 0.08 0.35 0.20 4.4 60 0.11 7 8 7.2 0.3 0.20 0.50 0.20 2.5 500.14 8 8 7.2 0.3 0.20 0.60 0.20 3.0 65 0.16 9 8 7.4 0.3 0.20 0.30 0.201.5 50 0.10 10 8 7.2 0.6 0.15 0.25 0.20 1.7 65 0.10 11 8 2.6 4.1 0.150.25 0.20 1.7 65 0.19 12 8 7.5 0.2 0.10 0.50 0.20 5.0 55 0.13 13 8 7.60.3 0.24 0.35 0.20 1.5 50 0.11 14 8 7.6 0.3 0.25 0.33 0.20 1.3 65 0.1115 8 7.7 0.1 0.20 0.40 0.30 2.0 15 0.20 16 8 7.7 0.1 0.20 0.40 0.40 2.05 0.22 17 8 7.4 0.3 0.20 0.40 0.10 2.0 50 0.09 18 8 7.1 0.5 0.20 0.400.06 2.0 60 0.07 19 3 7.2 0.6 0.20 0.40 0.20 2.0 0 0.20 20 15 7.7 0.10.20 0.40 0.20 2.0 50 0.08 21 8 7.6 0.3 0.20 0.40 0.20 2.0 15 0.13 22 87.6 0.3 0.20 0.40 0.20 2.0 20 0.11 23 8 7.7 0.3 0.20 0.40 0.20 2.0 150.13 24 8 7.4 0.3 0.20 0.40 0.16 2.0 30 0.10 25 8 7.7 0.1 0.20 0.40 0.242.0 15 0.15 26 8 7.2 0.3 0.17 0.50 0.20 2.9 55 0.14 27 18 7.7 0.1 0.200.40 0.20 2.0 55 0.06 28 8 3.0 2.1 0.20 0.40 0.20 2.0 15 0.12 1-1 8 7.40.3 0.40 0.80 1.00 2.0 80 0.30 1-2 8 7.5 0.2 0.20 0.80 1.00 4.0 50 0.281-3 8 2.6 4.3 0.40 0.80 1.00 2.0 80 0.35 1-4 8 2.4 4.4 0.20 0.80 1.004.0 50 0.33 1-5 3 7.5 0.2 0.20 0.80 1.00 4.0 20 0.35 1-6 15 7.5 0.2 0.200.80 1.00 4.0 70 0.23 1-7 8 7.6 0.3 0.20 0.80 1.00 4.0 45 0.35 1-8 8 7.70.3 0.20 0.80 1.00 4.0 50 0.33 1-9 8 7.7 0.3 0.20 0.80 1.00 4.0 45 0.35

<Cutting Evaluation 1>

A cutting test was performed under the following cutting conditions 1using each of the cutting tools obtained above. For twenty differentcutting edges, cutting was performed with each of the cutting edges for20 seconds, and each of the cutting edges was checked for the presenceor absence of fracture(s), wherein “fracture” means that a chip(s) of500 μm or more is (are) observed. The proportion of the cutting edgeshaving the fracture(s) occurring of the twenty cutting edges wascalculated to obtain the fracture rate (%). That is, the fracture rate(%)=(number of cutting edges having the fracture(s) occurring/20)×100.When the fracture rate is 55% or less, the cutting tool is judged tohave excellent fracture resistance and to have a long tool life. Theresults are shown in the column “Cutting evaluation 1—Fracture rate (%)”in Table 5.

(Cutting Conditions 1)

Material to be cut: SCM440 (grooved round bar)

Machining: intermittent turning of the outer diameter of a grooved roundbar

Cutting speed: 120 m/min

Feed amount: 0.1 mm/rev

Cut amount: 2.0 mm

Cutting fluid: None

The above cutting conditions correspond to high-efficiency machining ofhigh-hardness steel.

<Cutting Evaluation 2>

A cutting test was performed under the following cutting conditions 2using each of the cutting tools obtained above. The average wear amountVb (mm) on the flank face side of the cutting tool after cutting for 15minutes was measured, wherein “average wear amount” means the lengthdetermined by averaging the distance from the ridge line to the end offlank face wear. When the average wear amount Vb is 0.21 mm or less, thecutting tool is judged to have excellent wear resistance and to have along tool life. The results are shown in the column “Cutting evaluation2—Vb (mm)” in Table 5.

(Cutting Conditions 2)

Material to be cut: SUJ2

Machining: turning of the outer diameter of a round bar

Cutting speed: 280 m/min

Feed amount: 0.1 mm/rev

Cut amount: 2.0 mm

Cutting fluid: water-soluble cutting oil

The above cutting conditions correspond to high-efficiency machining ofhigh-hardness steel.

<Discussions>

The cutting tools of Specimens 1 to 3, Specimen 5, Specimen 7, Specimen9, Specimen 12, Specimen 13, Specimen 15, Specimen 17, and Specimens 19to 28 correspond to Examples. The specimens of these Examples wereconfirmed to have excellent fracture resistance and wear resistance andto have a long tool life. Particularly, it was confirmed that the effectof improving wear resistance was extremely excellent against such wearas flank wear that uniformly occurs.

Each of the specimens of the above Examples has the particle diameter ofthe α-Al₂O₃ particles gradually increasing from the base material sidetoward the tool surface side in the region on the base material side ofthe α-Al₂O₃ layer. Therefore, the particle diameter of the α-Al₂O₃ layernear the tool surface is smaller than that of the conventional tool, butthe crack propagation distance from the tool surface is long, and it ispresumed that cracks in the region on the base material side of theα-Al₂O₃ layer are inhibited from extending and the fracture resistanceis thereby good.

Specimen 1 and Specimen 2 have the same thickness of the α-Al₂O₃ layer.The average particle diameter a, the average particle diameter b and theaverage particle diameter c of Specimen 1 are the same as the averageparticle diameter a, the average particle diameter b and the averageparticle diameter c of Specimen 2. In Specimen 1, TC (0 0 12) is largerthan TC (110). In Specimen 2, TC (110) is larger than TC (0 0 12).Specimen 1 was confirmed to be more excellent in wear resistance thanSpecimen 2. On the other hand, Specimen 2 was confirmed to be moreexcellent in fracture resistance than Specimen 1. From the above, whenthe thickness of the α-Al₂O₃ layer and the average particle diameter aof the first region, the average particle diameter b of the secondregion and the average particle diameter c of the third region were thesame, it was confirmed that the larger the TC (0 0 12) was, the more thewear resistance was improved whereas the larger the TC (110) was, themore the fracture resistance was improved. This tendency is alsoconfirmed by the comparison between Specimen 10 and Specimen 11.

Specimen 4, Specimen 6, Specimen 8, Specimen 10, Specimen 11, Specimen14, Specimen 16, Specimen 18 and Specimens 1-1 to 1-9 correspond toComparative Examples. These Specimens had insufficient fractureresistance and/or wear resistance and had a short tool life.

Although the embodiments and Examples of the present disclosure havebeen described above, the configurations of the above-describedembodiments and examples are contemplated from the beginning to beappropriately combined or variously modified.

The embodiments and Examples disclosed herein should be considered asexemplary and not as restrictive in all respects. The scope of thepresent invention is specified by the claims rather than the embodimentsand examples described above, and is intended to include meaningsequivalent to the claims and to include all modifications within thescope thereof.

REFERENCE SIGNS LIST

-   1, 21, 31, 41: cutting tool; 10: base material, 11: α-Al₂O₃ layer;    12: underlayer; 13: surface layer; 14: interlayer; 15, 25, 35, 45:    coating; A1: first region; A2: second region; A3: third region; P1,    P3: interface; P2: surface, S1, S2, S3: virtual surface; B1: peak    portion of P1; T1: bottom portion of P1; LS1: reference line; L1,    L2: line.

The invention claimed is:
 1. A cutting tool comprising a base materialand a coating arranged on the base material; wherein: the coatingcomprises an α-Al₂O₃ layer; the α-Al₂O₃ layer is composed of a pluralityof α-Al₂O₃ particles; the α-Al₂O₃ layer comprises a first region, asecond region and a third region; the first region is a regionsandwiched between an interface P1 on the base material side of theα-Al₂O₃ layer and a virtual surface S1 that is located at a distance of0.5 μm from interface P1 toward the surface side of the coating; thesecond region is a region sandwiched between virtual surface S1 and avirtual surface S2 that is located at a distance of 1.0 μm from virtualsurface S1 toward the surface side of the coating; the third region is aregion sandwiched between a surface P2 of the α-Al₂O₃ layer or aninterface P3 on the surface side of the coating of the α-Al₂O₃ layer anda virtual surface S3 that is located at a distance of 1.0 μm fromsurface P2 or from interface P3 toward the base material side; theaverage particle diameter a of the α-Al₂O₃ particles in the first regionis 0.10 μm or more and 0.30 μm or less; the average particle diameter bof the α-Al₂O₃ particles in the second region is 0.30 μm or more and0.50 μm or less; the average particle diameter c of the α-Al₂O₃particles in the third region is 0.10 μm or more and 0.30 μm or less;and the ratio b/a between the average particle diameter b and theaverage particle diameter a is 1.5 or more and 5.0 or less.
 2. Thecutting tool according to claim 1, wherein the average particle diameterc is 0.16 μm or more and 0.24 μm or less.
 3. The cutting tool accordingto claim 1, wherein the ratio b/a is 1.5 or more and 2.5 or less.
 4. Thecutting tool according to claim 1, wherein the average thickness of theα-Al₂O₃ layer is 3 μm or more and 15 μm or less.
 5. The cutting toolaccording to claim 1, wherein the α-Al₂O₃ layer has a TC (0 0 12) of 3or more in an orientation index TC (hkl).